As an exhaust gas purification system for purifying NOx contained in engine exhaust gas, an exhaust gas purification apparatus described in Japanese Patent No. 3283868 (Patent Document 1) is proposed. The exhaust purification apparatus injection-supplies a liquid reducing agent or a precursor thereof at a flow rate according to an engine operating state, to an exhaust upstream side of an SCR (Selective Catalytic Reduction) catalyst disposed in an engine exhaust passage. The exhaust purification apparatus thus selectively causes a reduction reaction of NOx in the exhaust gas using the SCR catalyst, thereby purifying NOx to a harmless component. Moreover, in the conventional exhaust gas purification apparatus, to promote mixing of the liquid reducing agent or the precursor thereof injection-supplied from an injector including an injection nozzle and the exhaust gas, a mixing device (mixer) is disposed in the exhaust passage between the injection nozzle and the SCR catalyst.